PubMed Health⌕ Search

Biomedical subjects

H E Lebovitz

Publications and source records attributed to H E Lebovitz.

At least 91 records · Page 5Linked to original sources
PubMed1980

Specific nuclear binding of adenosine 3',5'-monophosphate-binding protein complex with subsequent poly(A) RNA synthesis in embryonic chick cartilage.

We used embryonic chick pelvic cartilage as a model to study the mechanism by which cyclic AMP increases RNA synthesis. Isolated nuclei were incubated with [32P]-8-azidoadenosine 3,5'-monophosphate ([32P]N3cAMP) with no resultant specific nuclear binding. However, in the presence of cytosol proteins, nuclear binding of [32P]N3cAMP was demonstrable that was specific, time dependent, and dependent on a heat-labile cytosol factor. The possible biological significance of the nuclear binding of the cyclic AMP-protein complex was identified by incubating isolating nuclei with either cyclic AMP or cytosol cyclic AMP-binding proteins prepared by batch elution DEAE cellulose chromatography (DEAE peak cytosol protein), or both, in the presence of cold nucleotides and [3H]uridine 5'-triphosphate. Poly(A) RNA production occurred only in nuclei incubated with cyclic AMP and the DEAE peak cytosol protein preparation. Actinomycin D inhibited the incorporation of [3H]uridine 5'-monophosphate into poly(A) RNA. The newly synthesized poly(A) RNA had a sedimentation constant of 23S. Characterization of the cytosol cyclic AMP binding proteins using [32P]N3-cAMP with photoaffinity labeling three major cAMP-binding complexes (41,000, 51,000, and 55,000 daltons). The 51,000 and 55,000 dalton cyclic AMP binding proteins were further purified by DNA-cellulose chromatography. In the presence of cyclic AMP they stimulated poly(A) RNA synthesis in isolated nuclei. The 51,000-dalton cyclic AMP-binding protein was the predominant one that bound to the nuclei. While cyclic AMP-dependent protein kinsae activity was present in the cytosol and DEAE peak cytosol proteins, it was not present in the DNA-cellulose-bound, cyclic AMP-binding proteins. We conclude that one possible mechanism by which cyclic AMP increases RNA synthesis is by complexing to a 51,000-dalton cytosol cyclic AMP-binding protein and being subsequently translocated to the nucleus, where it is specifically bound and associated with induction of poly(A) RNA synthesis.

Animals↗
PubMed1980

Hormone responsiveness of a transplantable rat chondrosarcoma. I. In vitro effects of growth hormone-dependent serum factors and insulin.

Serum somatomedins and insulin stimulate transport processes and macromolecular synthesis in cartilage. The in vitro effects of serum somatomedins and insulin on amino acid transport and macromolecule synthesis in the Swarm rat chondrosarcoma were studied to determine if malignant transformation alters the responsiveness of chondrocytes to these factors. Amino acid transport was assessed by alpha-aminoisobutyrate uptake. Macromolecule synthesis was estimated by radiolabeled precursor incorporation into RNA, total proteins, and proteoglycan. Serum from normal rats and GH-treated hypophysectomized rats stimulates alpha-aminoisobutyrate uptake and macromolecule synthesis in the rat chondrosarcoma. Hypophysectomized rat serum stimulates these events marginally or not at all. Thus, the chondrosarcoma responds in vitro to GH-dependent serum factors. Additionally, insulin stimulates in vitro amino acid transport and macromolecule synthesis in the rat chondrosarcoma. These data demonstrate that, in vitro, the Swarm rat chondrosarcoma is a hormone-responsive tumor.

Aminoisobutyric Acids↗
PubMed1980

Hormone responsiveness of a transplantable rat chondrosarcoma. II. Evidence for in vivo hormone dependence.

We have previously demonstrated that the Swarm rat chondrosarcoma responds to GH-dependent serum factors in vitro by increasing amino acid transport and macromolecular synthesis. The question of in vivo hormone dependence was evaluated by studying the growth of the tumor in hypophysectomized rats. Tumor-bearing hypophysectomized rats were treated with saline, T4, cortisone, bovine GH (bGH), or combinations of these hormones. Tumor growth was assessed in terms of tumor weight. Histological appearance was studied to ascertain the viability of the tumors and the relative contributions of cellularity vs. cartilage matrix to the weight of the chondrosarcoma. The weight of tumors grown in saline-treated hypophysectomized rats was less than 10% of the weight attained by tumors grown in normal rats for a comparable period of time. There was a greater relative cellularity in tumors grown in normal and hormone-treated hypophysectomized rats compared to that in tumors grown in saline-treated hypophysectomized rats. Tumors from saline-treated hypophysectomized rats had an atrophic appearance. Treatment of the hypophysectomized rats with bGH or cortisone increased the rate of tumor growth 5- to 6-fold and restored the histological appearance toward that of tumors grown in normal rats. A greater rate of tumor growth was effected by treatment with a combination of bGH and cortisone. T4 by itself did not stimulate chondrosarcoma growth in the hypophysectomized rat. Withdrawal of bGH and cortisone treatment from hypophysectomized rats after tumors were hormone stimulated caused a loss of the apparent exponential rate of growth observed in hypophysectomized rats treated through the full 38-day observation period. These data indicate that bGH and cortisone act in concert to stimulate the growth of the Swarm rat chondrosarcoma in vivo and that the tumor is hormone dependent.

Animals↗
PubMed1979

Adenosine 3',5'-monophosphate effects on cartilage ribonucleic acid synthesis.

We have previously shown that N6-monobutyryl-cAMP stimulates the incorporation of radiolabeled precursors into the macromolecules of embryonic chicken cartilage incubated in organ culture. The present study assessed the specific effects of N6-monobutyryl-cAMP on RNA synthesis in the cartilage organ culture system. The data show that treatment of cartilage with N6-monobutyryl-cAMP results in a coordinated stimulation of mRNA, rTNA, and tRNA synthesis. Incubation of cartilage with N6-monobutyryl-cAMP causes an increase of [5-3H]uridine incorporation into poly A-containing cartilage RNA and 28S, 18S, and 4S RNA as well. Increased incorporation of the radiolabeled nucleotide occurs without a measurable change in uridine triphosphate specific activity or in the rate of RNA degradation. Further, the isolated poly A-containing RNA directs protein synthesis in an in vitro cell-free system, and stimulation of cartilage mRNA by N6-monobutyryl-cAMP does not alter the size distribution of the mRNA species synthesized from that present in control tissue. These data indicate that cAMP enhances cartilage transcriptional activity. In addition, the increased synthesis of mRNA occurs antecedent to demonstrable effects on protein synthesis. Thus, the effects of cAMP on protein synthesis may be secondary to action at the nucleus.

Animals↗
PubMed1979

The insulin receptor of embryonic chicken cartilage.

Highly purified plasma membranes have been obtained from embryonic chicken cartilage by physical means rather than enzymatic digestion. Rapid and reversible binding of [125I]iodoinsulin to these membranes is demonstrated. Similar to the insulin-binding properties of rat liver and adipocytes and human mononuclear cells, optimal specific binding of insulin to chondrocyte plasma membranes has a sharp pH optimum at 8.0, and maximal binding occurs at 2--4 C. Analysis of equilibrium binding reveals a curvilinear Scatchard plot, whose high affinity segment generates a maximum affinity of 1.0 X 10(9) M-1, and a receptor concentration of 0.4 pmol/mg membrane protein. This affinity constant is similar to those generated for insulin binding to membranes prepared from embryonic chicken liver (2.5 X 10(9) M-1), rat liver (1.4 X 10(9) M-1), and mouse liver (0.6 X 10(9) M-1), whereas the receptor concentration is less than that of embryonic chicken liver membranes (1.1 pmol/mg), which in turn was less than those of rat liver membranes (2.8 pmol/mg) and mouse liver membranes (3.5 pmol/mg). Kinetic studies show augmentation of insulin-receptor dissociation by excess insulin when initial receptor occupancy, is low, suggesting that negative cooperativity is present. There is little or no interaction of other hormones with the chondrocyte insulin receptor, with the exception of proinsulin and the insulin-like growth factors. Porcine proinsulin, bovine proinsulin, somatomedin C, and nonsuppressible insulin-like protein prevent [125I]iodoinsulin binding to chondrocyte plasma membranes with dose-response curves which are parallel to that of unlabeled porcine insulin itself, but with molar potencies relative to porcine insulin of 15%, 9%, 2.5%, and 1.4%, respectively. Porcine insulin and proinsulin both prevent binding of [125I]iodosomatomedin C to chondrocyte plasma membranes but with molar potencies less than 1% that of unlabeled somatomedin C. These observations are consistent with the presence of a specific independent insulin receptor in embryonic chicken cartilage which is similar in its characteristics to the insulin receptor in previously described tissues. Insulin has a weak interaction with the chondrocyte receptor for somatomedin C. Interaction with the somatomedin receptor may be the mechanism by which insulin exerts anabolic effects on cartilage when used in pharmacological amounts.

Animals↗
PubMed1979

Sulfonylurea drugs and insulin-independent diabetes mellitus.

Insulin-independent diabetes is a disease characterized by insulin resistance and the patient's concomitant inability to compensate by exaggerated insulin secretion. A primary abnormality in the plasma membrane of the afflicted cells may cause both of these phenomena. Recent studies investigating the mechanism of action of sulfonylurea drugs show that these agents probably exert their antidiabetic action by increasing insulin sensitivity and ameliorating the insulin resistance, rather than by increasing insulin secretion. Dietary treatment alone, though effective in lowering the FPG level, does not ameliorate the insulin resistance of insulin-independent diabetes mellitus. Thus, sulfonylurea drugs appear to be rational therapeutic agents for the treatment of this form of diabetes. Clinical studies confirm the beneficial effects of these drugs in controlling the hyperglycemia of insulin-independent diabetes. Major unresolved questions are (1) Why do primary and secondary failures occur? (2) Is the underlying membrane abnormality progressive? (3) How long are sulfonylureas effective? (4) What is the mechanism of the membrane disturbance and how do sulfonylureas ameliorate it? (5) Do sulfonylureas drugs cause cardiovascular toxicity? The answers to these questions will provide further insight into our understanding of insulin-independent diabetes and will lead to the development of better drugs for its treatment. In the meantime, sulfonylureas are rational agents for the therapy for this disorder, if they are used appropriately.

Adult↗
PubMed1978

Primary hyperparathyroidism in paraneoplastic hypercalcaemia.

Hypercalcaemia is often associated with malignant disease. Causes of elevated serum-calcium levels in the absence of bony metastases include parathyroid-hormone production by the tumour, osteolytic factors made by the tumour, and coexistent primary hyperparathyroidism. By measuring nephrogenous cyclic-A.M.P. excretion to assess parathyroid-hormone function, we have determined the mechanism of such hypercalcaemia in 15 patients. Nephrogenous cyclic A.M.P. ranges from 0.05 to 2.40 mumol/g of creatinine in normal subjects, from 2.27 to 8.45 mumol/g in patients with primary hyperparathyroidism, and from 0.50 to 1.30 mumol/g in patients with proven non-hyperparathyroid hypercalcaemia without malignancy. 9 patients (60%) with hypercalcaemia and malignancy had normal levels of nephrogenous cyclic A.M.P. (range 0.35-2.07 mumol/g creatinine). The other 6 (40%) had elevated nephrogenous cyclic A.M.P. (range 2.70-5.55 mumol/g) consistent with increased parathyroid-hormone secretion. Surgical exploration of the neck in these patients showed that the increased parathyroid-hormone secretion was secondary to primary hyperparathyroidism, not ectopic hyperparathyroidism. Thus, the data indicate that coexistent hyperparathyroidism may be common in patients with hypercalcaemia and malignancy and that the measurement of nephrogenous cyclic A.M.P. is very useful in identifying patients at risk for hyperparathyroidism.

Adenocarcinoma↗
PubMed1978

Measurement of plasma adenosine 3',5'-monophosphate.

Currently used methods for plasma cAMP measurements are either tedious (chromatographic preparation of sample) or potentially inaccurate (direct assay of plasma samples). A rapid, simple, and accurate competitive binding assay for plasma cAMP, which does not require chromatographic preparation of the sample, has been developed. This procedure prevents destruction of plasma cAMP by utilizing both theophylline and EDTA in the collection of the blood sample. Human plasma contains variable amounts of cAMP-binding activity which interfere with the measurement of cAMP by the standard competitive binding assay. Our assay procedure removes this binding activity by precipitation of plasma proteins with perchloric acid. The normal fasting value (+/- SD) of plasma cAMP using this technique is 17.6 +/- 4.3 pmol/ml, which is identical to values obtained by methods utilizing chromatographic purification of samples (18.3 +/- 3.0). The fasting plasma cAMP of patients with hyperparathyroidism is normal (16.2 +/- 3.4), but patients with maturity-onset diabetes mellitus have fasting values significantly below normal (12.3 +/- 2.4).

Animals↗
PubMed1978

Hypothalamic insufficiency: the cause of hypopituitarism in sarcoidosis.

Ten patients with generalized sarcoidosis and hypopituitarism were studied. Six of these 10 patients presented with sarcoid involvement of the optic nerves resulting in asymmetric visual field defects. All patients had deficiencies of two or more anterior pituitary hormones and seven had abnormalities of water metabolism. Despite hypopituitarism, nine patients had a pituitary responsive to the synthetic hypothalamic releasing factors, thyrotropin releasing hormone and gonadotropin releasing hormone, and the tenth patient had a partially responsive pituitary. The demonstration of pituitary responsiveness allows us to infer hypothalamic insufficiency as the major cause for hypopituitarism in these patients. The combination of visual field defects and hypopituitarism in sarcoidosis is a medically treatable condition that simulates the clinical presentation of a pituitary tumor.

Adolescent↗
PubMed1977

Amino acid dependent and independent insulin stimulation of cartilage metabolism.

The effects of insulin on embryonic chicken cartilage in organ culture and the dependence of these effects on essential amino acids have been studied. In the presence of all essential amino acids, insulin: (1) increases 2-deoxy-D-glucose and alpha-aminoisobutyric acid uptake; (2) increases [5(-3H] uridine flux into uridine metabolites and the intracellular UTP pool; (3) expands the size of the intracellular UTP pool; (4) does not change the specific activity of the UTP pool; and (5) stimulates RNA, proteoglycan, and total protein synthesis. In lysine (or other essential amino acid)-deficient medium, the effects of insulin are different. While insulin stimulates incorporation of [5(-3)H] uridine into RNA, it does so by increasing the specific activity of the UTP pool without increasing RNA synthesis. Insulin stimulates 2-deoxy-D-glucose and alpha-aminoisobutyric acid uptake but no longer stimulates proteoglycan, total protein, or RNA synthesis or expands the size of the UTP pool. These data indicate that there are amino acid dependent and independent effects of insulin on cartilage. Transport processes are amino acid independent, while synthetic processes are amino acid dependent.

Aminoisobutyric Acids↗
PubMed1977

Hypoparathyroidism: a possible cause of osteomalacia .

A 17 year old man with longstanding hypocalcemia and hyperphosphatemia presented with incapacitating bone pain and progressive weakness nad bowing of the legs. The serum abnormalities were due to idiopathic hypoparathyroidism as evidenced by a decreased serum concentration of parathyroid hormone and an appropriate rise in urinary cyclic AMP and phosphate excretion, and serum calcium concentration, in response to exogenously administered parathyroid extract. The serum concentration of 1,25-dihydroxycholecalciferol was appropriately decreased. The bone findings were due to osteomalacia as documented by physical findings, bone roentgenograms, and bone biopsy. Normal renal tubular function, blood pH, and serum concentration of 25-hydroxycholecalciferol and elevated serum alkaline phosphatase excluded the common causes of osteomalacia. The data are consistent with the hypothsis that lack of parathyroid hormone causes both hypocalcemia and a decreased serum concentration of 1,25-dihydroxycholecalciferol which, in turn, limit the availability of calcium and cause defective synthesis of bone matrix resulting in abnormal mineralization.

Adolescent↗
PubMed1977

Potentiation of insulin action: a probable mechanism for the anti-diabetic action of sulfonylurea drugs.

Insulin action was assessed by measuring insulin-mediated glucose disposal (KI) in 13 non-ketotic diabetic patients both before treatment and after normalization of plasma glucose by diet (5 patients) or sulfonylurea (glipizide) therapy (8 patients). While the KI of the diet-treated group was unchanged by therapy, that of the glipizide-treated group was significantly increased. The data show that chronic glipizide therapy is associated with a potentiation of insulin action, which may account for the major anti-diabetic effect of this drug.

Adult↗
PubMed1976

Stimulation of cartilage macromolecule synthesis by adenosine 3',5'-monophosphate.

The role of cyclic AMP in the regulation of cartilage macromolecule synthesis in vitro was studied in pelvic cartilage from 10-12 day chick embryos. Incubation of cartilages in medium containing 0.5 mM cyclic AMP resulted in a 30% inhibition of 35SO4-2, [3H]leucine and [3H]uridine incorporation into proteoglycan, total protein and RNA, respectively. Higher concentrations of cyclic AMP had no greater effects. In contrast, butyrylated cyclic AMP derivatives (0.5-5.0 mM) added to the incubation medium stimulated (50-100%) the incorporation of these radiolabeled precursors into cartilage macromolecules. Theophylline, in concentrations (0.1-0.5 mM) which raise intracellular cyclic AMP, also increases the incorporation of radiolabeled precursors into macromolecules. The data indicate that exogenous cyclic AMP and butyrylated cyclic AMP derivatives have paradoxical effects on cartilage macromolecule synthesis. Butyrylated cyclic AMP derivatives, not exogenous cyclic AMP, mimic the effects of intracellular cyclic AMP. Incubation of embryonic chicken cartilage with exogenous cyclic AMP results in the extracellular degradation of the cyclic AMP to adenosine. Adenosine (0.125 mM) inhibits precursor incorporation into cartilage macromolecules. The metabolism of exogenous cyclic AMP generates sufficient adenosine to account for the observed inhibitory effects of exogenous cyclic AMP on cartilage macromolecule synthesis. Butyrylated cyclic AMP derivatives are not degraded during incubation with cartilage. The data indicate that cartilage is a tissue in which the effect of cyclic AMP is to stimulate anabolic processes.

Animals↗
PubMed1976

Levodopa-stimulated growth hormone secretion and diabetic retinopathy.

Since growth hormone has been implicated as a possible etiologic factor in the development of diabetic retinopathy, we examined growth hormone levels in two groups of growth-onset diabetics matched for age and duration of disease. The experimental group had definite proliferative diabetic retinopathy; the control group of growth-onset diabetics had no significant retinopathy. Basal and levodopa-stimulated levels of growth hormone were determined for each group. Growth hormone response could not be correlated with the presence or absence of diabetic retinopathy (P less than .05).

Adult↗
PubMed1976

Renal cyclic adenosine monophosphate: an accurate index of parathyroid function.

Measurement of total urine cyclic 3':5'-adenosine monophosphate (cyclic AMP) only incompletely discriminates between normal, hyperparathyroid, and nonparathyroid hypercalcemic patients. Only a fraction of total urine cyclic AMP is contributed by parathyroid hormone (PTH) action on the proximal nephron (renal cyclic AMP); the remainder is derived from plasma by glomerular filtration. We dtermined total urine and plasma cyclic AMP and PTH (by carboxy-terminal specific radioimmunoassay) in control, hyperparathyroid, nonparathyroid hypercalcemic, and surgically hypoparathyroid patients. Renal cyclic AMP was calculated as total urine cyclic AMP minus the filtered component. Of these determinations, only renal cyclic AMP segregated normal from hyperparathyroid, and hyperparathyroid from nonparathyroid hypercalcemic patients with complete accuracy. These data suggest that measurement of renal cyclic AMP provides an accurate index of parathyroid activity and allows clinical discrimination and appropriate treatment of the sub-groups of patients with malignancy and nonparathyroid hypercalcemia from those with hyperparathyroidism.

Adult↗